Microwave dielectric ceramic composition

Abstract: The present invention provides a microwave dielectric ceramic composition in which ε r, Qu and τ f are generally controlled within a practical characteristic range and each of the characteristics is maintained in a well balanced state. A ceramic composition of the present invention comprises a composition represented by xBi₂O₃-(1-x)(yNb₂O₅-(1-y)Ta₂O₅) in which 0.45 ≦ x≦ 0.55 and 0.1≦y<1.0 as a main ingredient, to which not more than 0.8 parts by weight of V₂O₅ is added and incorporated. An another ceramic composition comprises a composition represented by Bi(NbxTa1-x)O₄ in which 0<x≦0.96 as a main ingredient, to which not more than 5wt% of V₂O₅ and not more than 2wt% of PbO are added and incorporated. An another ceramic composition comprises the main ingredient as described above to which not more than 5wt% of V₂O₅ and not more than 2wt% of MnO₂ are added and incorporated. An another ceramic composition comprises the main ingredient as described above to which not more than 2wt% of V₂O₅ and not more than 1wt% of TiO₂ are added and incorporated. An another ceramic composition comprises the main ingredient as described above, to which not more than 2wt% of V₂O₅, not more than 2wt% of MnO₂ and not more than 0.7wt% of TiO₂ are added and incorporated. Instead of TiO₂ described above, not more than 0.5wt% (particularly not more than 0.4wt%) of PbO can be added and incorporated.

Description: BACKGROUND OF THE INVENTION The present invention concerns a microwave dielectric ceramic composition and, more in particular, it relates to a microwave dielectric ceramic composition having a temperature coefficient of a resonance frequency (hereinafter simply referred to as τ f) varied generally within a practical characteristic range while maintaining a practical unload Q (hereinafter simply referred to Qu) and a greatly improved specific dielectric constant (hereinafter simply referred to as ε r). The present invention also concerns a microwave dielectric ceramic composition in which each of the characteristics is balanced at a practical level. The present invention further concerns a microwave dielectric ceramic composition in which ε r and Qu are controlled generally within a practical characteristic range while maintaining τ f at a practical high level and each of the characteristics is balanced at a high level. The present invention further concerns a microwave dielectric ceramic composition in which ε r, Qu and τ f are controlled generally within a practical characteristic range and each of the characteristics is maintained in a well balanced state. The present invention is utilized for impedance matching or the like of dielectric resonators, microwave integrated circuit substrate, various kinds of microwave circuits in a microwave region and it is particularly suitable to LC filter materials. Generally, LC filter materials, dielectric resonators, dielectric substrates used in the high frequency region such as microwaves or millimetre wavelengths are required to have high ε r and high Qu, as well as small absolute value for the temperature coefficient of the resonance frequency. Namely, since the dielectric loss of a microwave dielectric ceramic composition (hereinafter simply referred to as dielectric ceramic composition) tends to increase as the working frequency becomes higher, a dielectric ceramic composition having large ε r and Qu in a microwave region is desired. For such a dielectric ceramic composition, a composition belonging to a composite perovskite structure such as Ba(Zn 1/3 Ta 2/3 )O 3 or Ba(Mg 1/3 Ta 2/3 )O 3 or BaO-TiO 2 system composition has been used in recent years, but all of them require a high sintering temperature of 1300 °C or higher. Such a high sintering temperature requires greater electric power consumption during sintering which results in a disadvantage regarding production cost or productivity. Further, in a case of sintering together with a conductor having a low melting point as an electrode, for example, silver (melting point: 961 °C) or copper (melting point: 1083°C) as in an LC filter or a strip line filter, it is particularly advantageous that the sintering temperature is lower than the melting point of the conductor. Accordingly, a material sinterable at a temperature as low as possible is demanded. SUMMARY OF THE INVENTION An object of the present invention is to provide a dielectric ceramic composition capable of having τ f varying generally within a practical range and high ε r while maintaining high Qu by a composition comprising a main ingredient of Bi 2 O 3 -Nb 2 O 5 -Ta 2 O 5 system and a predetermined amount of V 2 O 5 added and incorporated thereto. The present inventor has made various studies on Bi 2 O 3 -Nb 2 O 5 -Ta 2 O 5 system compositions having τ f varied generally within a practical characteristic range while maintaining high Qu, having high ε r and capable of being produced by sintering at a low temperature and, as a result, has accomplished the present invention based on the discovery that the foregoing object can be attained by varying the ratio between Nb 2 O 5 and Ta 2 O 5 in the above-mentioned composition and, further, adding a predetermined amount of V 2 O 5 thereto. That is, the dielectric ceramic composition according to the present invention comprises a composition represented by xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ) in which 0.45 ≦ x≦ 0.55 and 0 < y < 1.0 as a main ingredient, to which not more than 0.8 parts by weight (not including 0 part by weight) of V 2 O 5 is added and incorporated based on 100 parts by weight of the xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ). In the above-mentioned invention, x is defined as 0.45 to 0.55, because Qu is too small if x is less than 0.45 or exceeds 0.55. Further, y is within a range: 0 < y < 1.0. If Nb 2 O 5 is not present (y = 0), the absolute value for τ f tends to increase (decrease in a negative direction) and ε r tends to decrease. If Nb 2 O 5 is present even in a small amount, ε r which is important for LC filter material tends to be improved. On the other hand if y is at 1.0, ε r tends to decrease and Qu tends to decrease as y increases. Further, the addition ratio of V 2 O 5 (α) is defined as not more than 0.8% by weight (not including 0% by weight), because Qu tends to decrease if it is added in excess of 0.8% by weight although the addition of V 2 O 5 can lower the sintering temperature. Further, the case in which α is 0% by weight, that is, of V 2 O 5 is not added, is excluded, because this makes sintering insufficient and lowers each of the characteristics. The addition amount of V 2 O 5 at 0.4% by weight is more preferred since Qu increases much higher as compared with the case of addition of 0.8% by weight, 0.6% by weight and 0.2% by weight (Nos. 5 - 8 compared with Nos. 13 - 16, Nos. 9 - 12 and 1 - 4 in Table 1). In particular, it is preferred that x is from 0.47 to 0.53, y is from 0.4 to 0.8 and α is from 0.4 to 0.6, since each physical property is balanced. In this case, ε r is from 42.9 to 47.7, Qu is from 790 to 1490 and τ f is from -46.4 to -16.2 ppm/ °C. Further, the dielectric ceramic composition of the present invention is produced as described below. Specifically, bismuth oxide (III) powder, niobium oxide (V) powder, tantalum oxide (V) powder and vanadium oxide (V) powder are mixed so as to provide a composition comprising a composition represented by xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ) in which 0.45 ≦ x≦ 0.55 and 0 < y < 1.0 as a main ingredient, to which not more than 0.8 parts by weight (not including 0 part by weight) of V 2 O 5 is added and incorporated based on 100 parts by weight of the xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ) and then calcined to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 860 - 950 °C. The sintering temperature is defined as within 860 to 950 °C, because Qu decreases and τ f increases excessively in the negative direction out of the temperature range. Further, low temperature sintering is particularly preferred in a case of sintering simultaneously with a conductor such as for an LC filter. The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. In the dielectric ceramic composition according to the present invention, τ f can be varied widely within a practical characteristic range while maintaining Qu at a level with no practical problem by setting each of the oxides to a predetermined ratio in the Bi 2 O 3 -Nb 2 O 5 -Ta 2 O 5 system, to which a predetermined amount of V 2 O 5 is added. Further, a dielectric ceramic composition having extremely high ε r and suitable to LC filter material can be obtained. Further, the dielectric ceramic composition according to the present invention can be prepared by sintering at a relatively low temperature as 860 to 950°C. Such low temperature sintering is particularly advantageous in a case of the LC filter which is sintered simultaneously with a conductor. An object of the present invention is to provide a dielectric ceramic composition in which Qu and τ f are controlled within a wide characteristic range while maintaining ε r at a high and each of the characteristics is balanced at a practical level, by with a composition comprising Bi(NbTa)O 4 as a main ingredient to which V 2 O 5 and PbO is added each in a predetermined amount. The present inventor has made various studies on Bi(NbTa)O 4 system compositions having Qu and τ f controlled within a wide practical characteristic range while maintaining high ε r and capable of being produced by sintering at a low temperature and over a broad temperature range and, as a result, has accomplished the present invention based on the discovery that the foregoing object can be attained by varying the ratio between Nb 2 O 5 and Ta 2 O 5 in the above-mentioned composition and, further, adding a predetermined amount of V 2 O 5 and PbO thereto. The dielectric ceramic composition of the present invention comprises a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient to which not more than 5% by weight (not including 0% by weight) of V 2 O 5 and not more than 2% by weight (not including 0% by weight) of PbO are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . In the above-mentioned invention, x is defined as: 0 < x≦ 0.96, because the Ta 2 O 5 ingredient is substantially absent if x exceeds 0.96, making it difficult to control ε r and τ f. Further, the addition amount of V 2 O 5 is defined as greater than 0 and not more than 5% by weight, because addition in excess of 5% by weight can not provide any further effect and it rather results in deterioration of other characteristics such as Qu, although the sintering temperature can be lowered by the addition of V 2 O 5 , and because sintering is insufficient to lower each of the characteristics if V 2 O 5 is not added. The addition amount of V 2 O 5 within a range from 0.2 to 2.0% by weight is more preferred since a practical dielectric ceramic composition showing well balanced in each of the characteristics can be obtained. Further, the addition amount of PbO is greater than 0 and not more than 2% by weight. Addition of PbO can increase ε r and Qu as compared with the case of not adding PbO at all. However, although ε r is improved in proportion with the addition amount of PbO, Qu reaches a peak at the addition amount of 0.2% by weight and tends to reduce beyond the peak, τ f tends to increase in the negative direction in proportion with the addition of PbO. This trend is remarkable if the addition amount is as great as 1 to 2% by weight. Accordingly, for obtaining a dielectric ceramic composition well balanced in each of the characteristics and having a high level, it is preferred that the addition amount of PbO is within a range from 0.1 to 1.0% by weight. Further, it is preferred that x is from 0.2 to 0.9 (table 1 and 2), the addition amount of V 2 O 5 is from 0.2 to 2.0% by weight and the addition amount of PbO is from 0.2 to 0.6% by weight (table 3). In this case, ε r is from 45 to 48, Qu is from 960 to 1640 (at from 3.6 to 4.0 GHz) and τ f is from -47 to -36 ppm/ °C. Further, the dielectric ceramic composition of the present invention is produced as described below. The predetermined metal oxide powders are mixed so as to provide a predetermined composition and then calcined to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 850 - 950°C. The sintering temperature is defined as within 850 to 950°C, because Qu decreases and τ f increases excessively in the negative direction out of the temperature range. Further, low temperature sintering is particularly preferred in the case of sintering simultaneously with a conductor such as for an LC filter. The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. In the dielectric ceramic composition according to the present invention, a dielectric ceramic composition well balanced in each of the characteristics such as Qu and τ f while maintaining practically high ε r and suitable to LC filter material can be obtained by setting each of the oxides at a predetermined ratio in the Bi(NbTa)O 4 system, to which V 2 O 5 and PbO are added each in a predetermined amount. Further, a composition of particularly excellent performance can be obtained in a range of relatively lower addition amount of PbO. Further, the dielectric ceramic composition according to the present invention can be prepared by sintering at a relatively low temperature over a broad temperature range such as 850 to 950°C. Such low temperature sintering is particularly advantageous in a case of the LC filter which is sintered simultaneously with a conductor. An object of the present invention is to provide a dielectric ceramic composition in which ε r and Qu are controlled widely within a practical characteristic range while maintaining τ f at a practically high level and each of the characteristics is balanced at a high level, by a composition comprising a Bi(NbTa)O 4 system as a main ingredient to which V 2 O 5 and MnO 2 are added and incorporated each by a predetermined amount. The present inventor has made various studies on Bi(NbTa)O 4 system compositions having ε r and Qu controlled widely within a practical characteristic range while maintaining practical high τ r and capable of being produced by sintering at a low temperature over a broad temperature range and, as a result, has accomplished the present invention based on the discovery that the foregoing object can be attained by varying the ratio between Nb 2 O 5 and Ta 2 O 5 in the above-mentioned composition and, further, adding a predetermined amount of V 2 O 5 and MnO 2 thereto. The dielectric ceramic composition according to the present invention comprises a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 5% by weight (not including 0% by weight) of V 2 O 5 and not more than 2% by weight (not including 0% by weight) of MnO 2 are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . Further, in the present invention, the addition amount of MnO 2 may be from 0.1 to 1.0% by weight based on 100% by weight of Bi(NbxTa1-x)O 4 . In the above-mentioned invention, x is defined as: 0 < x≦ 0.96, because the Ta 2 O 5 ingredient is substantially absent if x exceeds 0.96, making it difficult to control ε r and τ f. Further, the addition amount of V 2 O 5 is defined as greater than 0 and not more than 5% by weight, because addition in excess of 5% by weight can not provide any further effect and it rather results in deterioration of other characteristics such as Qu, although the sintering temperature can be lowered by the addition of V 2 O 5 , and because sintering is insufficient to lower each of the characteristics if V 2 O 5 is not added. The addition amount of V 2 O 5 within the range from 0.2 to 2.0% by weight is more preferred since a practical dielectric ceramic composition with well balanced characteristics can be obtained. The addition amount of MnO 2 is more than 0 and not more than 2% by weight and the addition of MnO 2 can improve all of τ f, ε r and Qu with a certain exception as compared with a case of not adding MnO 2 at all. However, although ε r is improved linearly in proportion with the addition mount of MnO 2 , τ f rather decreases depending on the case as the addition amount of τ f exceeds 1% by weight, particularly, as the sintering temperature goes higher, while Qu reaches a peak at the addition amount of 0.2% by weight and tends to lower beyond the peak. Accordingly, for obtaining a dielectric ceramic composition well balanced in each of the characteristics at a high level, it is preferred that the addition amount of MnO 2 is within a range from 0.1 to 1.0% by weight . Further, it is preferred that x is from 0.2 to 0.9 (tables 1 and 2), the addition amount of V 2 O 5 is from 0.2 to 2.0% by weight and the addition amount of MnO 2 is from 0.1 to 0.6% by weight (table 4). In this case, ε r is from 45 to 47, Qu is from 970 to 1640 (at from 3.6 to 3.9 GHz) and τ f is from -14 to -5.5 ppm/°C. Further, the dielectric ceramic composition of the present invention is produced as described below. The predetermined metal oxide powders are mixed so as to provide a predetermined composition and then calcined to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 850 - 950°C. The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. The sintering temperature is defined as within 850 to 950 °C, because Qu decreases and τ f increases excessively in the negative direction out of the temperature range. Further, low temperature sintering is particularly preferred in a case of sintering simultaneously with a conductor such as for an LC filter. In the dielectric ceramic composition according to the present invention, a dielectric ceramic composition well balanced in each of the characteristics such as ε r and Qu while maintaining practically high τ f and suitable to LC filter material can be obtained by setting each of the oxides at a predetermined ratio in the Bi(NbTa)O 4 system, to which V 2 O 5 and MnO 2 are added each in a predetermined amount. Further, a composition of particularly excellent performance can be obtained in a range of relatively lower addition amount of MnO 2 . Further, the dielectric ceramic composition according to the present invention can be prepared by sintering at a relatively low and wide temperature as 850 to 950°C. Such low temperature sintering is particularly advantageous in a case of the LC filter which is sintered simultaneously with a conductor. An object of the present invention is to provide a microwave dielectric ceramic composition in which ε r, Qu and τ f are controlled widely within a practical characteristic range and each of the characteristics is maintained in a well balanced state, by a composition comprising Bi(NbTa)O 4 system as a main ingredient to which V 2 O 5 and TiO 2 are added each in a predetermined amount. The present inventor has made various studies on Bi(NbTa)O 4 system compositions having ε r, Qu and τ f cotroled within a wide practical characteristic range and capable of being produced by sintering at a low temperature and, as a result, has accomplished the present invention based on the discovery that the foregoing object can be attained by varying the ratio between Nb 2 O 5 and Ta 2 O 5 in the above-mentioned composition and, further, adding a predetermined amount of V 2 O 5 and TiO 2 thereto, and in particular the discovery that the foregoing object can be attained by controlling τ f by an addition of TiO 2 . The dielectric ceramic composition according to the present invention comprises a composition represented by Bi(NbxTa1-x)O 4 ) in which 0 < x ≦ 0.96 as a main ingredient to which not more than 2% by weight (not including 0% by weight) of V 2 O 5 and not more than 1% by weight (not including 0% by weight) of TiO 2 are added and incorporated based on 100% by weight of the Bi(NbxTa1-x)O 4 ). In the above-mentioned invention, x is defined as: 0 < x≦ 0.96, because the Ta 2 O 5 ingredient is substantially absent if x exceeds 0.96, making it difficult to control ε r and τ f. By varying the addition amount of Ta 2 O 5 , control for ε r and τ f is facilitated and, particularly, by increasing the addition amount of Ta 2 O 5 , ε r and Qu can be increased. Further, the addition amount of V 2 O 5 is determined as more than 0 but not more than 2% by weight, because V 2 O 5 functions as a sintering aid and, accordingly, can lower the sintering temperature and stabilize the performance by the addition, but addition in excess of 2% by weight decreases Qu and τ f, whereas no addition of V 2 O 5 makes sintering insufficient and decreases each of the characteristics. The addition amount of V 2 O 5 , particularly, within a range from 0.3 to 0.5% by weight (particularly around 0.4% by weight) is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics is obtained. Further, the addition amount of TiO 2 is defined as not more than 1% by weight, because each of the characteristics decreases remarkably if the addition amount exceeds about 1% by weight. TiO 2 has an effect of transferring τ f from a negative to positive direction by the addition and an addition amount within a range from 0.1 to 0.3% by weight (particularly, 0.2% by weight) is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics is obtained. Further, x is from 0.6 to 0.96, the addition amount of V 2 O 5 may be from 0.2 to 1.0% by weight and the addition amount of TiO 2 may be from 0.1 to 0.6% by weight. This is because well balanced performance can be obtained for ε r, Qu and τ f within such a range of addition. Further, a practical balanced performance such as τ f from -30 to 0 ppm/°C, Qu from 510 to 1160, ε r from 42 to 48 can be obtained with the above-mentioned composition. Further, the dielectric ceramic composition of the present invention is produced as described below. The predetermined metal oxide powders are mixed so as to provide a predetermined composition and then calcined at 600 - 800 °C to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 875 - 950°C The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. The sintering temperature is defined as within 875 to 950 °C, because a sintering temperature of less than 875 °C may make sintering insufficient, a sufficient sintering density is ensured by sintering within this sintering range and the performance is stabilized. Further, low temperature sintering is particularly preferred when sintering simultaneously with a conductor such as for an LC filter. In the dielectric ceramic composition according to the present invention, ε r, Qu and τ f are within a practical characteristic range and each of the characteristics is maintained in a well balanced state. Accordingly, it is suitable as an LC filter material. Further, the dielectric ceramic composition according to the present invention can be prepared by sintering at a relatively low temperature over as broad a temperature range as 875 to 950°C. Such low temperature sintering is particularly advantageous in a case of the LC filter which is sintered simultaneously with a conductor. An object of present invention is to provide a microwave dielectric ceramic composition in which ε r, Qu and τ f are controlled within a wide practical characteristic range and each of the characteristics is maintained in a well balanced state, by a composition comprising a Bi(NbTa)O 4 system as a main ingredient, to which V 2 O 5 and MnO 2 , as well as TiO 2 or PbO are added and incorporated each in a predetermined amount. The present inventor has made various studies on Bi(NbTa)O 4 system compositions having ε r, Qu and τ f controlled widely within a practical characteristic range and capable of being produced by sintering at a low temperature and, as a result, has accomplished the present invention based on the discovery that the foregoing object can be attained by varying the ratio between Nb 2 O 5 and Ta 2 O 5 in the above-mentioned composition and, further, adding a predetermined amount of V 2 O 5 , MnO 2 and TiO 2 (or PbO) thereto. The dielectric ceramic composition according to the present invention comprises a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 2% by weight (not including 0% by weight) of V 2 O 5 , not more than 2% by weight (not including 0% by weight) of MnO 2 and not more than 0.7% by weight (not including 0% by weight) of TiO 2 are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . In the above-mentioned invention, x is defined as: 0 < x≦ 0.96, because the Ta 2 O 5 ingredient is substantially absent if x exceeds 0.96, making it difficult to control ε r and τ f. Since V 2 O 5 functions as a sintering aid, addition thereof can lower the sintering temperature and stabilize the performance. If the addition amount of V 2 O 5 exceeds 2% by weight, it decreases Qu and τ f, whereas if V 2 O 5 is not added, sintering is insufficient to decrease each of the characteristics. An addition amount of V 2 O 5 , particularly, from 0.2 to 1.0% by weight (preferably, from 0.3 to 0.5% by weight, more preferably, about 0.4% by weight) is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics can be obtained. For instance, at the addition amount: (1) from 0.2 to 1.0% by weight (MnO 2 and TiO 2 : both 0.2% by weight, x: 0.8), ε r is 46.6 to 47.9, Qu is 890 to 1300 as τ f is - 10.91 to -2.45 ppm/ °C and (2) addition amount of 0.4% by weight (MnO 2 and TiO 2 : both 0.2% by weight, x: 0.8), ε r is 47.1, Qu is 1325 and τ f is -7.46 ppm/ °C. Further, both of Qu and τ f are improved by the addition of MnO 2 up to 0.4% by weight. Accordingly, since MnO 2 has an effect of transferring τ f from negative to positive direction within this addition range, it is effective to adjust τ f from negative to positive direction. On the other hand, if it is added by more than 2% by weight, it is not preferred since Qu tends to decrease greatly. Particularly, an addition amount of not more than 1.0% by weight is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics can be obtained. For instance, at the addition amount of from 0.2 to 1.0% by weight (V 2 O 5 ; 0.4% by weight, TiO 2 ; 0.2% by weight, x; 0.8), ε r is 47.0 to 47.5, Qu is 900 to 1440 and τ f is -6.0 to -11.1 ppm/ °C. Further, the addition amount of TiO 2 is defined as not more than 0.7% by weight, because Qu is decreases greatly and τ f transfers in the positive direction apart from 0 if the addition amount is more than 0.7% by weight. Since TiO 2 has an effect of transferring τ f from negative to positive direction by the addition, it is effective for adjusting τ f from negative to positive direction. Particularly, a practical dielectric ceramic composition well balanced in each of the characteristics can be obtained with an addition amount of 0.1 to 0.2% by weight. For instance, at the addition amount from 0.1 to 0.2% by weight (V 2 O 5 ; 0.4% by weight, MnO 2 : 0.2% by weight and x: 0.8), ε r is 46.4 to 47.1, Qu is 1320 to 1490 and τ f is - 8.8 to -7.5 ppm/°C. Further, it is possible to set the addition amount of V 2 O 5 as 0.2 to 1.0% by weight, the addition amount of MnO 2 of not more than 1.0% by weight and the addition amount of TiO 2 of not more than 0.4% by weight and x as 0.8 to 0.96, because the performance is well balanced in this case. For instance, it is possible to attain τ f: -12 to +7 ppm/ °C, Qu: 800 to 1600 and ε r: 45 to 50. Further, the dielectric ceramic composition of the present invention is produced as described below. The predetermined metal oxide powders are mixed so as to provide a predetermined composition and then calcined at 600 - 800 °C to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 850 - 950°C . The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. The sintering temperature is defined as within 850 to 950 °C, because Qu decreases and τ f increases excessively in the negative direction out of the temperature range. Further, low temperature sintering is particularly preferred in a case of sintering simultaneously with a conductor such as for an LC filter. A dielectric ceramic composition according to the present invention comprises a composition represented by Bi(NbxTa1-x)O 4 , in which 0 < x ≦ 0.96 as a main ingredient, to which 0.2 to 1% by weight of V 2 O 5 , not more than 1% by weight (not including 0% by weight) of MnO 2 and not more than 0.5% by weight (not including 0% by weight) of PbO are added and incorporated. The reason why x is defined as 0 < x≦ 0.96 in this invention is identical with the reason explained for the first invention. Further, since V 2 O 5 functions as a sintering aid, addition thereof can lower the sintering temperature and stabilize the performance. If the addition amount exceeds 1% by weight, Qu decreases and it decreases remarkably to about 510 at the addition amount of 3% by weight. Further, if the addition amount exceeds 1% by weight, τ f is not more than -24 ppm/ °C, that is, increases toward the negative direction. Further, if V 2 O 5 is not added sintering is insufficient and Qu decreases, which is not desired. The addition amount of V 2 O 5 , particularly, from 0.4 to 0.8% by weight is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics can be obtained. For instance, (1) at the addition amount of from 0.4 to 0.8% by weight (x: 0.8, MnO 2 and PbO: both 0.2% by weight), ε r is 44.9 to 46.8, Qu is 1460 to 1950 as τ f is -14.5 to -1.7 ppm/ °C and (2) addition amount of 0.6% by weight (x: 0.8, MnO 2 and PbO: both 0.2% by weight), ε r is 46.5, Qu is 1430 and τ f is - 1.75 ppm/ °C and τ f is nearly 0. Further, addition of MnO 2 can increase ε r and τ f. Since the addition of this ingredient has a function of transferring particularly, τ f from negative to positive direction, so that it is effective for adjusting τ f from negative to positive direction. On the other hand, if addition amount is more than 1% by weight, Qu tends to decrease remarkably, which it is not preferred. Particularly, the addition amount of MnO 2 from 0.2 to 0.4% by weight (V 2 O 5 ; 0.4% by weight, PbO; 0.2% by weight and x; 0.8) is preferred since this can provide a practical dielectric ceramic composition well balanced in each of the characteristics as ε r: 46.8 to 47.9, Qu: 1351 to 1465 and τ f: -6.3 to -2.1 ppm/°C. Further, the addition amount of PbO is defined as not more than 0.5% by weight, because Qu and τ f decrease greatly if the addition amount is more than 0.5% by weight. Since PbO has an effect of transferring, particularly, τ f from positive to negative direction by the addition, it is effective for adjusting τ f from positive to negative direction. Particularly, the addition amount of PbO from 0.2 to 0.4% by weight (V 2 O 5 : 0.4% by weight, MnO 2 : 0.2% by weight and x: 0.8) is more preferred since a practical dielectric ceramic composition well balanced in each of the characteristics can be obtained as ε r: 46.8 to 47.4, Qu: 1293 to 1465, τ f; -13.2 to -6.3 ppm/ °C. Further, it is possible to set the addition amount of V 2 O 5 as 0.3 to 0.8% by weight, the addition amount of MnO 2 as 0.1 to 1.0% by weight, the addition amount of PbO as not more than 0.4% by weight and x as from 0.8 to 0.96, because the performances are well balanced in this case. For instance, it is possible to attain τ f; -15 to +4 ppm/°C, Qu: 1000 to 2000 and ε r: 44 - 49. Further, the dielectric ceramic composition of the present invention is produced as described below. The predetermined metal oxide powders are mixed so as to provide a predetermined composition and then calcined at 600 - 800 °C to prepare a calcined powder, which is pulverized, molded into a predetermined shape and then sintered at 850 - 950°C . The sintering temperature is defined as within 850 to 950 °C , because Qu decreases and τ f increases excessively in the negative direction out of the temperature range. Further, low temperature sintering is particularly preferred in a case of sintering simultaneously with a conductor such as for an LC filter. The sintering can be carried out either in an ambient atmosphere or a reducing atmosphere. In the dielectric ceramic composition according to the present invention, ε r, Qu and τ f are within a practical characteristic range and each of the characteristics is maintained in a well balanced state. Accordingly, it is suitable to the LC filter material. Further, the dielectric ceramic composition according to the present invention can be prepared by sintering at a relatively low temperature over as broad a temperature range as 850 to 950°C. Such low temperature sintering is particularly advantageous in a case of the LC filter which is sintered simultaneously with a conductor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relation between x and ε r in (the main ingredient represented by xBi 2 O 3 -(1-x) (0.8Nb 2 O 5 -0.2Ta 2 O 5 ) + 0.4% by weight of V 2 O 5 ). Fig. 2 is a graph showing the relation between x and Qu in (the main ingredient represented by xBi 2 O 3 -(1-x) (0.8Nb 2 O 5 -0.2Ta 2 O 5 ) + 0.4% by weight of V 2 O 5 ). Fig. 3 is a graph showing the relation between x and τ f in (the main ingredient represented by xBi 2 O 3 -(1-x) (0.8Nb 2 O 5 -0.2Ta 2 O 5 ) + 0.4% by weight of V 2 O 5 ). Fig. 4 is a graph showing the relation between y of the main ingredient represented by 0.5Bi 2 O 3 -0.5(yNb 2 O 5 -(1-y) Ta 2 O 5 ) and ε r for different values of the addition amount (α) of V 2 O 5 . Fig. 5 is a graph showing the relation between y of the main ingredient represented by 0.5Bi 2 O 3 -0.5(yNb 2 O 5 -(1-y) Ta 2 O 5 ) and Qu for different values of the addition amount (α) of V 2 O 5 . Fig. 6 is a graph showing the relation between y of the main ingredient represented by 0.5Bi 2 O 3 -0.5(yNb 2 O 5 -(1-y) Ta 2 O 5 ) and τ f for different values of the addition amount (α) of V 2 O 5 . Fig. 7 is a graph showing the relation between the sintering temperature and ε r for different values of the addition amount (δ) of PbO, in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 8 is a graph showing the relation between the sintering temperature and Qu for different values of the addition amount (δ) of PbO, in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 ) O 4 + 0.4% by weight of V 2 O 5 ). Fig. 9 is a graph showing the relation between the sintering temperature and τ f for different values of the addition amount (δ) of PbO, in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 10 is a graph showing the relation between the sintering temperature and the sintering density for different values of the addition amount ( δ ) of PbO, in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 11 is a graph showing the relation between the addition amount ( δ ) of PbO and ε r in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900°C. Fig. 12 is a graph showing the relation between the addition amount ( δ ) of PbO and Qu in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900°C. Fig. 13 is a graph showing the relation between the addition amount ( δ ) of PbO and τ f in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900°C. Fig. 14 is a graph showing the relation between the addition amount ( δ ) of PbO and the sintering density in (the main ingredient represented by Bi(Nb 0.6 Ta 0.4 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900°C. Fig. 15 is a graph showing the relation between the sintering temperature and ε r for different values of the addition amount ( β ) of MnO 2 , in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 16 is a graph showing the relation between the sintering temperature and Qu for different values of the addition amount ( β ) of MnO 2 , in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 17 is a graph showing the relation between the sintering temperature and τ f for different values of the addition amount ( β ) of MnO 2 , in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 18 is a graph showing the relation between the sintering temperature and the sintering density for different values of the addition amount ( β ) of MnO 2 , in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ). Fig. 19 is a graph showing the relation between the addition amount ( β ) of MnO 2 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900°C. Fig. 20 is a graph showing the relation between the addition amount ( β ) of MnO 2 and Qu in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900 °C. Fig. 21 is a graph showing the relation between the addition amount ( β ) of MnO 2 and τ f in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900 °C. Fig. 22 is a graph showing the relation between the addition amount ( β ) of MnO 2 and the sintering density in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900 °C. Fig. 23 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 ) for a sintering temperature of 900 °C. Fig. 24 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and Qu for the ceramic composition and the sintering temperature in Fig. 23. Fig. 25 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and τ f for the ceramic composition and the sintering temperature in Fig. 23. Fig. 26 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and the sintering density for the ceramic composition and the sintering temperature in Fig. 23. Fig. 27 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.2% by weight of TiO 2 ) for a sintering temperature of 900 °C. Fig. 28 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and Qu for the ceramic composition and the sintering temperature in Fig. 27. Fig. 29 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and τ f for the ceramic composition and the sintering temperature in Fig. 27. Fig. 30 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and the sintering density for the ceramic composition and the sintering temperature in Fig. 27. Fig. 31 is a graph showing the relation between x and ε r in (the main ingredient represented by Bi(Nbx Ta1-x )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of TiO 2 ) for a sintering temperature of 900 °C. Fig. 32 is a graph showing the relation between x and Qu for the ceramic composition and the sintering temperature in Fig. 31. Fig. 33 is a graph showing the relation between x and τ f for the ceramic composition and the sintering temperature in Fig. 31. Fig. 34 is a graph showing the relation between x and the sintering density for the ceramic composition and the sintering temperature in Fig. 31. Fig. 35 is a graph showing the relation between the sintering temperature and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of TiO 2 ). Fig. 36 is a graph showing the relation between the sintering temperature and Qu for the ceramic composition in Fig. 35. Fig. 37 is a graph showing the relation between the sintering temperature and τ f for the ceramic composition in Fig. 35. Fig. 38 is a graph showing the relation between the sintering temperature and the sintering density for the ceramic composition in Fig. 35. Fig. 39 is a graph showing the relation between the addition amount (α) of V 2 O 5 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.2% by weight of MnO 2 + 0.2% by weight of TiO 2 (or PbO)) for a sintering temperature of 900 °C. Fig. 40 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and Qu for the ceramic composition and the sintering temperature in Fig. 39. Fig. 41 is a graph showing the relation between the addition amount ( α ) of V 2 O 5 and τ f for the ceramic composition and the sintering temperature in Fig. 39. Fig. 42 is a graph showing the relation between the addition amount (α) of V 2 O 5 and the sintering density for the ceramic composition and the sintering temperature in Fig. 39. Fig. 43 is a graph showing the relation between the addition amount( β ) of MnO 2 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of TiO 2 (or PbO)) for a sintering temperature of 900 °C. Fig. 44 is a graph showing the relation between the addition amount ( β ) of MnO 2 and Qu for the ceramic composition and the sintering temperature in Fig. 43. Fig. 45 is a graph showing the relation between the addition amount ( β ) of MnO 2 and τ f for the ceramic composition and the sintering temperature in Fig. 43. Fig. 46 is a graph showing the relation between the addition amount (β) of MnO 2 and the sintering density for the ceramic composition and the sintering temperature in Fig. 43. Fig. 47 is a graph showing the relation between the addition amount( γ ) of TiO 2 and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of MnO 2 ) for a sintering temperature of 900 °C. Fig. 48 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and Qu for the ceramic composition and the sintering temperature in Fig. 47. Fig. 49 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and τ f for the ceramic composition and the sintering temperature in Fig. 47. Fig. 50 is a graph showing the relation between the addition amount ( γ ) of TiO 2 and the sintering density for the ceramic composition and the sintering temperature in Fig. 47. Fig. 51 is a graph showing the relation between the addition amount (δ) of PbO and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of MnO 2 ) for a sintering temperature of 900 °C. Fig. 52 is a graph showing the relation between the addition amount (δ) of PbO and Qu for the ceramic composition and the sintering temperature in Fig. 51. Fig. 53 is a graph showing the relation between the addition amount (δ) of PbO and τ f for the ceramic composition and the sintering temperature in Fig. 51. Fig. 54 is a graph showing the relation between the addition amount (δ) of PbO and the sintering density for the ceramic composition and the sintering temperature in Fig. 51. Fig. 55 is a graph showing the relation between x and ε r in (the main ingredient represented by Bi(Nbx Ta1-x )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of MnO 2 + 0.2% by weight of TiO 2 (or PbO)) for a sintering temperature of 900 °C. Fig. 56 is a graph showing the relation between x and Qu for the ceramic composition and the sintering temperature in Fig. 55. Fig. 57 is a graph showing the relation between x and τ f for the ceramic composition and the sintering temperature in Fig. 55. Fig. 58 is a graph showing the relation between x and the sintering density for the ceramic composition and the sintering temperature in Fig. 55. Fig. 59 is a graph showing the relation between the sintering temperature and ε r in (the main ingredient represented by Bi(Nb 0.8 Ta 0.2 )O 4 + 0.4% by weight of V 2 O 5 + 0.2% by weight of MnO 2 + 0.2% by weight of TiO 2 (or PbO)). Fig. 60 is a graph showing the relation between the sintering temperature and Qu for the ceramic composition in Fig. 59. Fig. 61 is a graph showing the relation between the sintering temperature and τ f for the ceramic composition in Fig. 59. Fig. 62 is a graph showing the relation between the sintering temperature and the sintering density for the ceramic composition in Fig. 59. DETAILED DESCRIPTION OF THE INVENTION EXAMPLES The present invention will be explained more specifically by way of examples. Example 1 Bi 2 O 3 powder (purity: 98.9%), Nb 2 O 5 powder (purity: 99.9%), Ta 2 O 5 powder (purity: 99.9%) and V 2 O 5 powder (purity: 99.5%) were used as the raw materials, and they are weighed and mixed each by a predetermined amount (about 600 g as the entire amount in each of the cases) so as to provide compositions in which x ranges from 0.43 to 0.57 and each of y and the addition amount of V 2 O 5 ( α % by weight) varies within a range of 0 to 1.0 in xBi 2 O 3 -(1-x) (yNb 2 O 5 -(1-y)Ta 2 O 5 ) as shown in Tables 1 and 2. Subsequently, the weighed and mixed raw material powders were applied with primary pulverization by a vibration mill (3 hours) and then calcined in an ambient atmosphere at 700°C for 2 hours. Then, an appropriate amount of an organic binder (15 g) and water (320 g) were added to each calcined powder and applied with secondary pulverization was conducted in a ball mill using alumina balls of 20 mm, at 90 rpm for 23 hours. Subsequently, they were pelletized by vacuum freeze drying (pressure: about 5.3 Pa (0.4 Torr), freezing temperature: -20 to -40 °C, drying temperature: 40 to 50°C, drying time: about 20 hours). The thus pelletized raw materials were molded at a pressure of 1 ton/cm 2 to obtain cylindrical molding products each of 19 mm × 10 mmt (height). Then, the molding products were degreased in [0.5Bi 2 O 3 -0.5 {yNb 2 O 5 -(1-y)Ta 2 O 5 } + αV 2 O 5 ] ceramic composition No. y α (V 2 O 5 ) (wt %) f 0 (GHz) Rel. dielect. const. ε r Qu τ f (ppm/°C) 1 0.2 0.2 4.4 33.2 703 -56.8 2 0.4 0.2 4.0 42.5 510 -49.0 3 0.6 0.2 3.9 43.5 443 -41.2 4 0.8 0.2 3.9 43.1 491 -28.0 5 0.2 0.4 3.9 44.7 1344 -53.1 6 0.4 0.4 3.9 45.9 1488 -46.4 7 0.6 0.4 3.8 46.2 1305 -32.8 8 0.8 0.4 3.9 44.6 1487 -18.5 9 0.2 0.6 3.8 47.1 1014 -52.1 10 0.4 0.6 3.8 47.7 897 -39.8 11 0.6 0.6 3.8 46.6 791 -29.6 12 0.8 0.6 3.9 45.6 816 -18.5 13 0.2 0.8 3.7 49.0 746 -51.1 14 0.4 0.8 3.7 49.0 590 -36.2 15 0.6 0.8 3.8 48.0 505 -25.0 16 0.8 0.8 3.9 45.7 598 -18.9 [xBi 2 O 3 -(1-x) {yNb 2 O 5 -(1-y)Ta 2 O 5 } + αV 2 O 5 ] ceramic composition No. x y α (V 2 O 5 ) (wt %) f 0 (GHz) Rel. dielect. const. ε r Qu τ f (ppm/°C) 17 0.43 0.8 0.4 4.0 41.6 243 -26.5 18 0.45 0.8 0.4 4.0 42.2 610 -18.0 19 0.47 0.8 0.4 4.0 42.9 1100 -16.2 20 0.49 0.8 0.4 3.9 44.0 1360 -17.3 21 0.51 0.8 0.4 3.9 45.0 1432 -23.1 22 0.53 0.8 0.4 3.9 44.8 1190 -27.0 23 0.55 0.8 0.4 4.0 43.9 780 -31.5 24 0.57 0.8 0.4 4.0 42.7 370 -38.0 25 0.5 0 0.2 4.6 30.8 829 -57.5 26 0.5 0 0.4 4.1 40.4 1115 -48.3 27 0.5 0 1.0 3.7 50.3 562 -36.5 28 0.5 1.0 0.2 4.1 42.3 476 -23.6 29 0.5 0.9 0.4 4.0 43.7 1450 -11.5 30 0.5 1.0 0.4 4.0 42.9 1504 -2.7 31 0.5 1.0 1.0 4.0 44.5 557 -6.2 32 0.5 0.4 0 4.9 29.8 203 -68.0 atmospheric air at 500°C for 3 hours and then sintered at 850 to 900°C for 2 hours to obtain sintering products. Finally, each of the sintering products was polished at both end faces into a cylindrical shape of about 16 mm x 8 mmt (height), further cleaned with a diluted solution comprising 5 parts of an aqueous detergent ("Eriese K-2000" manufactured by Asahi Kasei Co.) and 100 parts of water mixed together, at 23°C for 60 min, and dried at 80°C for 10 hours to form dielectric specimens (Nos. 1 - 32 in Tables 1 and 2). The temperature elevation rate was 200 °C/h and the temperature lowering rate was -200 °C/h in the calcining step, the temperature elevation rate was 50 °C/h in the degreasing step, and the temperature elevation rate was 100 °C/h and the temperature lowering rate was -100 °C/h in the sintering step. Then, ε r, Qu and τ f were measured for each of the specimens by a parallel conductor plate dielectric columnar resonator method (TE 011 MODE) or the like. The resonance frequency upon measurement is as shown in Table 1 (f 0 ). Further, τ f was measured at a temperature region from 23 to 80°C and calculated according to τ f = (f 80 - f 23 )/(f 23 xΔT) and ΔT = 80 - 23 = 57°C. The results are shown in Tables 1 and 2 and in the graphs of Figures 1 to 6. From the results, Qu decreases remarkably at x for 0.43 and 0.57 and ε r also decreases considerably at x for 0.43 (No. 17 in Table 2) and τ f also decreases in the negative direction at x for 0.57 (No. 24 in Table 2). On the other hand it can be seen that within a range of x from 0.45 to 0.55, particularly, from 0.47 to 0.51, compositions excellent in all of ε r, Qu and τ f and well balanced in the characteristics is obtained (Figs. 1 - 3). Further, ε r slightly decreases at y = 1.0 and at α of 0.2% by weight (No. 28 in Table 2) and 0.4% by weight (No. 30 in Table 2) as compared with a case of y at 0.2 to 0.8. And if y is 0.9 and α is 0.4% by weight (No. 29 in Table 2), balance of ε r, Qu and τ f is exellent. If y is 0, ε r decreases further. Further, if y is 0, and α is 1.0 % by weight (No. 27 in Table 2), although ε r is excellent, Qu tends to decrease. Further, if y is 1.0, and α is 1.0% by weight (No. 31 in Table 2), although τ f is excellent, Qu decreases. If y is 0.4 and α is 0 (No. 32 in Table 2), all ε r, Qu and τ f greatly decrease because sintering is insufficient (Figs. 4 - 6). In each of the examples described above, although each of the performances ε r, Qu and τ f is excellent individually, balance between each of them is somewhat poor. On the other hand, if y is in a range of 0.2 to 0.8 and α is 0.8 % by weight (Nos. 13 - 16 in Table 1) and 0.6 by weight (Nos. 9 - 12 in Table 1), ε r is excellent. Although Qu decreases if α is 0.8% by weight but it is within a range causing no practical problems. Further, τ f also exhibits a practically sufficient performance with no problem. Further, if y is within a range from 0.2 to 0.8 and α is 0.4 % by weight (Nos. 5 to 8 in Table 1), although ε r tends to decrease slightly as compared with the case of α at 0.8 % and 0.6% by weight, Qu is improved greatly and τ f is equivalent, to show well balanced excellent performance. Furthermore, if y is within a range from 0.2 to 0.8 and α is 0.2% by weight (Nos. 1 - 4 in Table 1), each of the characteristics tends to decrease as compared with the case of greater α, but they are within a practically sufficient range (Figs. 4 to 6). In particular, as shown in results of tables 1 and 2, it is preferred that x is from 0.47 to 0.53, y is from 0.4 to 0.8 and α is from 0.4 to 0.6, since each physical property is balanced. In this case, ε r may be from 42.9 to 47.7, Qu may be from 790 to 1490 and τ f may be from - 46.4 to -16.2 ppm/ °C. Further, it can be seen from Figs. 4 to 6, that each of the characteristics exhibits a substantially identical trend as y increases from 0.2 to 0.8 irrespective of the value α and, particularly, the performance τ f tends to be improved, and the value τ f can be controlled within a practical value while maintaining high ε r and Qu with no practical problem, by varying the ratio of Nb 2 O 5 and Ta 2 O 5 . Example 2 As the raw material in this example, PbO powder (purity: 99.5%) was added further to each of the powders used in Example 1. Then, the starting materials were weighed and mixed in the same manner as in Example 1 so as to obtain a composition in which x is 0.6, the addition amount of V 2 O 5 is 0.4% by weight and the addition amount of PbO (δ % by weight) varies within a range from 0 to 2.0 in Bi(NbxTa1-x)O 4 as shown in Table 3. In Table 3, x is 0.2 in No. 13, the addition amount of V 2 O 5 is 3.0% by weight in No. 14, and x is 0.2 and the addition amount of V 2 O 5 is 3.0% by weight in No. 15. Further, in the same manner as in Example 1, dielectric specimens of identical shape (Nos. 1 to 30 in Table 3) were obtained and performance evaluation ( ε r, Qu, τ f and sintering density) was carried out. The results are also shown in Table 3 and shown in the graphs of Figs. 7 to 14. The sintering products were cleaned after polishing at 80 °C for 30 min and then dried subsequently at 100°C for 4 hours. The resonance frequency upon measurement is as shown in Table 3 (f 0 ). τ f was measured within a temperature region of 25 to 80°C and calculated according to τ f = (f 80 - f 25 )/(f 25 × ΔT) , and ΔT = 80 - 25 = 55°C. From the results, ε r is improved from about 45 to about 51 along with an increase in the addition amount of PbO irrespective of the sintering temperature except for the case of 42.05 at a sintering temperature of 850°C and the No. Sinter. temp. (°C) x V 2 O 5 (α) (wt%) PbO (δ) (wt%) f 0 (GHz) ε r Qu τ f (ppm/°C) Sint. density (g/cm 3 ) 1 850 0.6 0.4 0 Resonance wave form is very weak. 6.81 2 0.6 0.4 0.2 3.98 42.05 1425 -42.10 7.49 3 0.6 0.4 0.4 3.83 46.19 1041 -47.22 7.86 4 0.6 0.4 1 3.83 46.08 487 -58.78 7.70 5 0.6 0.4 2 3.75 48.06 193 -60.38 7.72 6 875 0.6 0.4 0 3.85 44.08 1607 -35.91 7.70 7 0.6 0.4 0.2 3.85 45.43 1640 -39.18 7.79 8 0.6 0.4 0.4 3.82 46.53 1213 -47.32 7.89 9 0.6 0.4 1 3.75 48.33 482 -53.06 7.91 10 0.6 0.4 2 3.67 50.38 238 -73.80 7.91 11 900 0.6 0.4 0 3.85 46.19 1304 -32.82 7.90 12 0.6 0.4 0.2 3.83 46.21 1528 -36.67 7.85 13 0.2 0.4 0.2 3.85 45.01 1511 -48.21 8.05 14 0.6 3.0 0.2 3.80 46.71 735 -42.33 7.95 15 0.2 3.0 0.2 3.83 46.40 594 -53.03 8.23 16 0.6 0.4 0.4 3.83 46.94 1211 -43.50 7.89 17 0.6 0.4 0.6 3.81 47.46 956 -47.80 7.90 18 0.6 0.4 0.7 3.80 47.71 828 -49.90 7.91 19 0.6 0.4 1 3.76 48.48 445 -56.27 7.93 20 0.6 0.4 2 3.65 51.37 280 -83.01 7.96 21 925 0.6 0.4 0 3.84 45.93 1255 -31.78 7.67 22 0.6 0.4 0.2 3.82 46.36 1423 -39.76 7.88 23 0.6 0.4 0.4 3.82 46.58 1192 -45.64 7.87 24 0.6 0.4 1 3.75 48.52 458 -56.87 7.92 25 0.6 0.4 2 3.64 51.45 240 -104.80 7.98 26 950 0.6 0.4 0 3.87 44.87 1214 -33.01 7.65 27 0.6 0.4 0.2 3.81 46.16 1378 -39.12 7.84 28 0.6 0.4 0.4 3.82 46.46 1094 -44.83 7.85 29 0.6 0.4 1 3.75 48.53 407 -62.61 7.91 30 0.6 0.4 2 3.63 51.69 214 -106.00 7.97 addition amount of PbO of 0.2% by weight (Fig.s 7 and 11). Improvement of Qu is observed if PbO is added by 0.2% by weight at each of the sintering temperatures as compared with the case of no addition, but it tends to decrease as the addition amount increases and, particularly, Qu decreases greatly at the addition amount of 1 to 2% by weight (the trend is shown clearly in Figs. 8 and 12). Further, τ f tends to increase toward the negative direction along with increase in the addition amount of PbO and the trend is particularly remarkable at the addition amount of 2% by weight (the trend is shown clearly in Figs. 9 and 13). From the abovementioned results, it is preferred that x is from 0.2 to 0.9 (tables 1 and 2), the addition amount of V 2 O 5 is from 0.2 to 2.0 part by weight and the addition amount of PbO is from 0.2 to 0.6% by weight (table 3). In this case, ε r may be from 45 to 48, Qu may be from 960 to 1640 (at from 3.6 to 4.0 GHz) and τ f may be from -47 to -32 ppm/°C. On the other hand, the sintering density takes a particularly small value in the case where PbO is not added and the sintering temperature is as low as 850 °C. In other cases, it slightly increases at each of the sintering temperatures along with the increase in the addition amount of PbO except for a certain case but no remarkable change is observed as a whole (it can be seen also in Figs 10 and 14). As described above, while each of the characteristics varies in accordance with the addition amount of PbO and the sintering temperature, each of the characteristics is within a range of causing no practical problem so long as they are within the range of the present invention. As a whole, it can be seen that most practically preferred dielectric ceramic compositions are obtained at a sintering temperature of 875°C or 900 °C, with the addition amount of PbO of 0.2 or 0.4% by weight since each of the characteristic is balanced most satisfactorily. Further, as can be seen from the results of Nos. 13 to 15, τ f tends to increase toward the negative direction if x is as small as 0.2 in the present invention, but dielectric ceramic compositions of excellent characteristics can be obtained according to the present invention within a wide range for x and the addition amount of V 2 O 5 . Example 3 For the raw material in this example, MnO 2 powder (purity: 96.0%) was used instead of the PbO powder used in Example 2. Then, the raw materials were weighed and mixed in the same manner as in Example 2 so as to obtain compositions in which x in Bi(NbxTa1-x)O 4 is 0.8, the addition amount of V 2 O 5 is 0.4% by weight and the addition amount of MnO 2 (β % by weight) ranges range from 0 to 2.0. In Table 4, x is 0.2 in No. 14, addition amount of V 2 O 5 is 3.0% by weight in No. 15, and x is 0.2 and addition No. Sinter. temp. (°C) x V 2 O 5 (α) (wt%) MnO 2 (β) (wt%) f 0 (GHz) ε r Qu τ f (ppm/°C) Sint. density (g/cm 3 ) 1 850 0.8 0.4 0 Resonance wave form is very weak. 7.08 2 0.8 0.4 0.2 3.84 45.85 1640 -11.61 7.52 3 0.8 0.4 0.4 3.81 46.83 1176 -9.76 7.52 4 0.8 0.4 1 3.75 48.62 715 -7.84 7.51 5 0.8 0.4 2 3.66 50.99 433 -5.50 7.48 6 875 0.8 0.4 0 3.86 44.45 1757 -18.73 7.47 7 0.8 0.4 0.2 3.84 46.01 1684 -11.75 7.52 8 0.8 0.4 0.4 3.82 46.93 1223 -9.91 7.53 9 0.8 0.4 1 3.75 48.71 729 -10.09 7.51 10 0.8 0.4 2 3.65 51.25 449 -8.31 7.48 11 900 0.8 0.4 0 3.92 44.60 1485 -18.47 7.48 12 0.8 0.4 0.1 3.89 45.17 1574 -14.32 7.49 13 0.8 0.4 0.2 3.86 45.74 1662 -10.16 7.50 14 0.2 0.4 0.2 3.88 44.72 1482 -53.10 8.13 15 0.8 3.0 0.2 3.82 46.31 681 -12.13 7.55 16 0.2 3.0 0.2 3.86 45.81 721 -62.31 8.24 17 0.8 0.4 0.4 3.83 46.85 1202 -8.34 7.51 18 0.8 0.4 0.6 3.80 47.40 1046 -7.81 7.50 19 0.8 0.4 0.7 3.79 47.68 968 -7.55 7.50 20 0.8 0.4 1 3.75 48.50 734 -6.76 7.49 21 0.8 0.4 2 3.65 51.45 476 -8.53 7.47 22 925 0.8 0.4 0 3.91 44.78 1319 -19.47 7.37 23 0.8 0.4 0.2 3.88 45.12 1680 -11.70 7.46 24 0.8 0.4 0.4 3.84 46.37 1163 -8.43 7.46 25 0.8 0.4 1 3.77 48.18 721 -9.38 7.44 26 0.8 0.4 2 3.65 51.02 445 -10.60 7.44 27 950 0.8 0.4 0 3.94 43.75 1245 -19.76 7.25 28 0.8 0.4 0.2 3.91 44.09 1668 -13.33 7.39 29 0.8 0.4 0.4 3.87 45.35 1181 -10.37 7.39 30 0.8 0.4 1 3.80 46.95 710 -9.26 7.35 31 0.8 0.4 2 3.67 50.50 418 -12.50 7.35 amount of V 2 O 5 is 3.0% by weight in No. 16 in Table 4. Further, in the same manner as in Example 2, dielectric specimens of identical shape (Nos. 1 to 31 in Table 4) were obtained and performance evaluation ( ε r, Qu, τ f and sintering density) was carried out. The resonance frequency upon measurement was as shown in Table 5 (f 0 ). The results are shown together in Table 4 and also shown in the graphs of Figs. 15 to 22. According to the results, τ f is extremely poor in the case of not adding MnO 2 and it is improved greatly by the addition of MnO 2 by 0.2% by weight. However, although τ f tends to improve slightly with further increase of the addition amount, it shows no great change (in Fig. 17, the curve for β = 0 is very different from the others, and other curves show no such great difference). This can be seen clearly also in Fig. 21). Further, ε r is improved from about 45 to about 51 along with the increase in the addition amount of MnO 2 irrespective of the sintering temperature (Figs.15 and 19). Further, although Qu tends to decrease along with increase in the addition amount of MnO 2 for a lower sintering temperature, it reaches a peak at the addition amount of 0.2% by weight as the sintering temperature goes higher and subsequently decreases a long with increase in the addition amount of MnO 2 (in Fig. 16, curves for β = 0 and β = 0.2 intersect with each other between 875°C and 900°C and Qu at β = 0.2 is higher in a high temperature region higher than 900 °C. Further, such a trend is also shown in Fig. 20 for the sintering temperature at 900°C). From the abovementioned results, it is preferred that x in Bi(Nb x Ta 1-x )O 4 is from 0.2 to 0.9 (table 1 and 2), the addition amount of V 2 O 5 is from 0.2 to 2.0 part by weight (table 4) and the addition amount of MnO 2 is from 0.1 to 0.6 wt% (table 4). In this case, ε r may be from 45 to 47, Qu may be from 970 to 1640 (at from 3.6 to 3.9 GHz) and τ f may be from -14 to -5.5 ppm/ °C. On the other hand, the sintering density takes a particularly small value if MnO 2 is not added and the sintering temperature is as low as 850 °C. In other cases where the sintering temperature is high, the sintering density is improved slightly by the addition amount of MnO 2 of 0.2% by weight at a higher sintering temperature and no remarkable changes is observed with addition amount of MnO 2 . Further, the sintering density tends to be lower as a whole, as the sintering temperature goes higher (this is shown clearly in Figs. 18 and 22). In this way, each of the characteristics changes variously along with the addition amount of MnO 2 and the sintering temperature, but each of the characteristics lies within a range of causing no practical problem so long as they are within a range of the present invention. It can be seen, as a whole, that preferred dielectric ceramic compositions well balanced in each of the characteristics can be obtained, particularly, at a sintering temperature of 875 °C or 900 °C and with the addition amount of MnO 2 of 0.2 or 0.4 by weight. Further, as can be seen from the results of Nos. 14 to 16, Table 4, τ f tends to increase toward the negative direction if x is as small as 0.2 in the present invention, but dielectric ceramic compositions having practically sufficient characteristics can be obtained in a wide range for x and the addition amount of V 2 O 5 . Example 4 For the raw material in this example, TiO 2 powder (purity: 99.9%) was used instead of the PbO powder used in Example 2. Then, the starting materials were weighed and mixed in the same manner as in Example 2 so as to obtain a composition in which x in Bi(NbxTa1-x)O 4 ranges from 0 to 1.0, the addition amount of V 2 O 5 (α % by weight) ranges from 0 to 3.0 and the addition amount of TiO 2 (γ % by weight) ranges from 0 to 2.0. Further, dielectric specimens of identical shape were prepared in the same manner as Example 2 (Nos. 1 to 23 in Table 5) and performance evaluation ( ε r, Qu, τ f and sintering density) was carried out. The resonance frequency upon measurement was as shown in Table 5 (f 0 ). The results are shown together in Table 5 and also shown in the graphs of Figs. 23 to 38. No. Sinter. temp. (°C) x V 2 O 5 (α) (wt%) TiO 2 (γ) (wt%) f 0 (GHz) ε r Qu τ f (ppm/°C) Sint. density (g/cm 3 ) 1 900 0.8 0.4 0 3.92 44.60 1485 -18.47 7.48 2 900 0.8 0.4 0.1 3.40 45.92 1155 -15.81 7.49 3 900 0.8 0.4 0.2 3.45 47.06 865 -12.24 7.51 4 900 0.8 0.4 0.4 3.38 47.48 678 -8.96 7.43 5 900 0.8 0.4 0.6 3.47 46.33 598 -2.38 7.23 6 900 0.8 0.4 1.0 3.52 43.37 371 10.61 6.89 7 900 0.8 0.4 2.0 3.54 37.39 251 53.78 6.89 8 850 0.8 0.4 0.2 Sintering is insufficient. 9 875 0.8 0.4 0.2 3.89 45.43 909 -12.27 7.36 10 925 0.8 0.4 0.2 3.40 47.16 838 -10.81 7.52 11 950 0.8 0.4 0.2 3.53 47.70 785 -11.76 7.52 12 900 0.8 0 0.2 Sintering is insufficient. 13 900 0.8 0.2 0.2 3.47 46.73 839 -13.55 7.50 14 900 0.8 1.0 0.2 3.35 47.62 613 -5.51 7.55 15 900 0.8 2.0 0.2 3.48 48.18 318 -13.94 7.53 16 900 0.8 3.0 0.2 3.60 49.01 185 -21.63 7.54 17 900 0 0.4 0.2 3.59 42.03 553 -52.13 8.08 18 900 0.2 0.4 0.2 3.53 44.54 512 -55.21 8.11 19 900 0.4 0.4 0.2 3.48 46.44 631 -48.03 8.05 20 900 0.6 0.4 0.2 3.41 47.21 725 -30.12 7.90 21 900 0.7 0.4 0.2 3.43 47.13 795 -21.18 7.70 22 900 0.96 0.4 0.2 3.45 46.11 1010 -0.11 7.15 23 900 1.0 0.4 0.2 3.23 45.86 1050 2.01 7.05 The results show that τ f improves greatly along with the addition amount of TiO 2 and τ f can be controlled easily (Fig. 25). However, since ε r and Qu decrease along with addition of TiO 2 (Figs. 23 and 24), addition of a great amount of TiO 2 is not preferred. Further, if V 2 O 5 is not added (No. 12), the sintering is insufficient and measurement for each of the characteristics is impossible. Then, since ε r increases (Fig. 27) and τ f decreases (Fig. 29) by the addition, τ f can be controlled. However, since Qu decreases by the addition (Fig. 28), addition of a great amount of V 2 O 5 is not preferred. Further, since τ f increases along with increase for the value x in Bi(NbxTa1-x)O 4 (Fig. 33), τ f can be controlled by the change of the value x. Further, since ε r and Qu also increase along with this increase (Figs. 31 and 32), although it is preferred in view of this physical property, the sintering density is lowered (Fig. 34). 7.0 kg/m 3 of sintering density can be ensured even if x is 1.0 (Fig. 34). Further, if the sintering temperature is 850 °C (No. 8 in Table 5), sintering is insufficient and measurement for each of the characteristics is impossible. On the other hand, at 875 to 950 °C (x = 0.8, V 2 O 5 = 0.4% by weight, TiO 2 = 0.2% by weight), the sintering density is as large as 7.36 to 7.52 kg/m 3 (Fig. 38) and the physical properties are also stable (Figs. 35 - 37). As described above, while each of the physical properties changes variously in accordance with the addition amounts of V 2 O 5 and TiO 2 and the sintering temperature, each of the characteristics lies within a range causing no practical problem so long as they are within a range of the present invention. For instance, in a case where x = 0.6 to 0.96, V 2 O 5 = 0.2 to 1.0% by weight and TiO 2 = 0.1 to 0.6% by weight, τ f = -30 to 0 ppm/ °C, Qu = 610 to 1160, ε r = 42 to 48. in the case where x = 0.8 to 0.96, V 2 O 5 = 0.4 to 1.0% by weight and TiO 2 = 0.2 to 1.0% by weight, ε r = 43.3 to 47.7, Qu = 370 to 910, τ f = -13 to + 11 ppm/°C. Particularly, in a case where x = 0.8, V 2 O 5 is 0.4% by weight, TiO 2 = 0.2 to 0.4% by weight, ε r = 45.4 to 47.7, Qu =510 to 910 and τ f = -13 to -9 ppm/°C, showing excellent balance of performance. As can be seen from the results of Nos. 18 to 20 in Table 5, although τ f tends to increase toward the negative direct ion (-55 to -30 ppm/°C) if x = as small as 0.2 to 0.6 in the present invention, ε r is from 42.0 to 47.2 and Qu is from 510 to 730, which are practically sufficient characteristics. Example 5 (1) Preparation of dielectric ceramic composition As the raw material in this example, TiO 2 powder (purity: 99.9%) or PbO powder (purity: 99.5%) was further used in addition to the powder used in Example 3. Then, the raw materials were weighed and mixed in the same manner as in Example 3 so as to obtain a composition in which x in Bi(NbxTa1-x)O 4 varies from 0 to 1.0, the addition amount of V 2 O 5 (α % by weight) varies from 0 to 3.0, the addition amount of MnO 2 ( β % by weight) varies from 0 to 2.0 and the addition amount of TiO 2 (γ % by weight, shown in Table 6) varies from 0 to 2.0 and, further, the addition amount of PbO ( δ % by weight, shown in Table 7) varies from 0 to 2.0, as shown in Tables 6 and 7. Further, in the same manner as in Example 3, dielectric specimens of identical shape (Nos. 1 to 27 in Table 6 and Nos. 1 to 29 in Table 7) were obtained and performance evaluation ( ε r, Qu, τ f and sintering density) was carried out. The resonance frequency upon measurement was as shown in Tables 6 and 7 (f 0 ). The results are shown together in Tables 6 and 7 and also shown in the graphs of Figures 39 to 62. (2) Effect of examples in V 2 O 5 -MnO 2 -TiO 2 system composition According to the results of Table 6 and Figs. 39 - 50 and Figs. 55 to 62, if V 2 O 5 is not added (No. 12 in Table 6) sintering is insufficient and measurement for each of the characteristics is impossible. Then, since ε r increases (Fig. 39) and τ f decreases (Fig. 41) along with addition, τ f can be controlled. However, since Qu decreases along with addition (Fig. 40), addition of a great No. Sinter temp. (°C) x α (V 2 O 5 ) (wt%) β (MnO 2 ) (wt%) γ (TiO 2 ) (wt%) f 0 (GHz) ε r Qu τ f (ppm/°C) Sint. density (g/cm 3 ) 1 900 0.8 0.4 0.2 0 3.86 45.74 1662 -10.16 7.50 2 900 0.8 0.4 0.2 0.1 3.40 46.40 1493 -8.81 7.51 3 900 0.8 0.4 0.2 0.2 3.35 47.06 1325 -7.46 7.53 4 900 0.8 0.4 0.2 0.4 3.38 48.57 747 -1.17 7.50 5 900 0.8 0.4 0.2 0.7 3.36 48.91 632 6.48 7.36 6 900 0.8 0.4 0.2 1.0 3.24 49.25 517 14.13 7.22 7 900 0.8 0.4 0.2 2.0 3.42 46.81 255 50.22 6.67 8 850 0.8 0.4 0.2 0.2 3.15 46.33 1618 -6.59 7.30 9 875 0.8 0.4 0.2 0.2 3.19 46.92 1461 -6.78 7.52 10 925 0.8 0.4 0.2 0.2 3.33 46.94 1319 -6.30 7.52 11 950 0.8 0.4 0.2 0.2 3.31 47.20 1282 -5.44 7.51 12 900 0.8 0 0.2 0.2 Sintering is insufficient. 13 900 0.8 0.2 0.2 0.2 3.41 46.63 1227 -10.91 7.50 14 900 0.8 1.0 0.2 0.2 3.35 47.88 893 -2.45 7.56 15 900 0.8 2.0 0.2 0.2 3.43 48.91 598 -9.03 7.50 16 900 0.8 3.0 0.2 0.2 3.41 49.04 417 -16.79 7.45 17 900 0.8 0.4 0 0.2 3.45 47.06 865 -12.24 7.51 18 900 0.8 0.4 0.4 0.2 3.31 47.23 1438 -6.03 7.50 19 900 0.8 0.4 1.0 0.2 3.44 47.46 903 -11.10 7.50 20 900 0.8 0.4 1.5 0.2 3.41 47.18 760 -11.46 7.46 21 900 0.8 0.4 2.0 0.2 3.40 46.89 618 -11.83 7.41 22 900 0 0.4 0.2 0.2 3.31 44.18 884 -48.23 8.08 23 900 0.2 0.4 0.2 0.2 3.24 45.90 1023 -49.58 8.13 24 900 0.4 0.4 0.2 0.2 3.43 47.16 1211 -44.35 7.98 25 900 0.6 0.4 0.2 0.2 3.41 47.51 1203 -25.11 7.73 26 900 0.96 0.4 0.2 0.2 3.27 46.02 1389 3.51 7.21 27 900 1.0 0.4 0.2 0.2 3.40 45.74 1415 6.34 7.05 No. Sinter. temp. (°C) x α (V 2 O 5 ) (wt%) β (MnO 2 ) (wt%) δ (PbO) (wt%) f 0 (GHz) ε r Qu τ f (ppm/°C) Sint. density (g/cm 3 ) * 1 900 0.8 0 0.2 0.2 Sintering is insufficient. 2 900 0.8 0.2 0.2 0.2 3.45 47.80 641 -12.90 7.57 3 900 0.8 0.3 0.2 0.2 3.44 47.30 1050 -9.60 7.55 4 900 0.8 0.4 0.2 0.2 3.47 46.81 1465 -6.28 7.53 5 900 0.8 0.6 0.2 0.2 3.42 46.53 1430 -1.75 7.51 6 900 0.8 0.8 0.2 0.2 3.47 44.88 1952 -14.46 7.46 7 900 0.8 1.0 0.2 0.2 3.45 43.75 1842 -23.14 7.42 8 900 0.8 2.0 0.2 0.2 3.46 42.49 1204 -35.03 7.35 9 900 0.8 3.0 0.2 0.2 3.40 41.80 513 -44.12 7.40 10 850 0.8 0.4 0.2 0.2 3.50 46.98 1523 -16.24 7.48 11 875 0.8 0.4 0.2 0.2 3.39 47.13 1468 -11.74 7.55 12 925 0.8 0.4 0.2 0.2 3.48 46.89 1388 -13.43 7.50 13 950 0.8 0.4 0.2 0.2 3.45 47.04 1399 -10.02 7.52 14 900 0.8 0.4 0 0.2 3.40 45.35 1604 -18.04 7.50 15 900 0.8 0.4 0.1 0.2 3.46 46.58 1520 -15.47 7.53 16 900 0.8 0.4 0.4 0.2 3.35 47.86 1351 -2.07 7.52 17 900 0.8 0.4 1.0 0.2 3.46 48.51 1047 -5.34 7.50 18 900 0.8 0.4 2.0 0.2 3.45 49.10 798 -12.95 7.53 19 900 0.8 0.4 0.2 0 3.86 45.74 1662 -10.16 7.50 20 900 0.8 0.4 0.2 0.4 3.65 47.39 1293 -13.24 7.49 21 900 0.8 0.4 0.2 0.5 3.36 47.42 1203 -15.70 7.49 22 900 0.8 0.4 0.2 1.0 3.54 48.48 753 -28.00 7.48 23 900 0.8 0.4 0.2 2.0 3.32 49.25 490 -49.57 7.45 24 900 0 0.4 0.2 0.2 3.45 43.81 1050 -44.03 8.07 25 900 0.2 0.4 0.2 0.2 3.41 45.99 1223 -48.15 8.09 26 900 0.4 0.4 0.2 0.2 3.40 46.75 1335 -39.95 8.00 27 900 0.6 0.4 0.2 0.2 3.47 47.01 1421 -23.42 7.75 28 900 0.96 0.4 0.2 0.2 3.40 45.89 1503 3.98 7.12 29 900 1.0 0.4 0.2 0.2 3.49 45.50 1530 5.15 7.04 amount of V 2 O 5 is not preferred. Further, since Qu increases along with addition of MnO 2 up to 0.4% by weight, the addition is effective, but addition of a great amount ( 1 and 2% by weight) is not preferred because Qu decreases greatly (Fig. 43). It is shown that τ f is improved greatly by addition of TiO 2 and τ f can be controlled easily (Fig. 49). Further, addition of TiO 2 up to 1.0% by weight is preferred since ε r increases (Fig. 47). Further, since Qu decreases by the addition of TiO 2 and, particularly, Qu decreases remarkably as 747 at 0.4% by weight, addition of a great amount of TiO 2 is not preferred (Fig. 48). Further, since τ f increases along with increase of the value x in Bi(NbxTa1-x)O 4 (Fig. 57), τ f can be controlled by the change of the x Further, since Qu increases along with increase of x (Fig. 56) and ε r also increases with x up to 0.6 (Fig. 55), it is preferred in view of this physical property, but the sintering density is lowered (Fig. 58). Further, 7.05 kg/m 3 of the sintering density can be insured even if x is 1.0 (No. 27, Fig. 58). Further, sintering is sufficient even at a sintering temperature of 850 °C (No. 8 in Table 6) and the sintering density is as great as 7.30 to 7.51 kg/m 3 at 850 - 950°C (x = 0.8, V 2 O 5 = 0.4% by weight, MnO 2 = 0.2% by weight and TiO 2 = 0.2% by weight) (Nos. 8 to 11 in Table 6, Fig. 62), and physical properties are also stable (Figs. 59 to 62). As described above, each of the characteristics changes variously in accordance with the kind of each of the additives, the addition amount thereof and the sintering temperature and well balanced practical performances as shown below are given, for example, with the range of the following compositions according to the results of this example (Table 6). (1) At V 2 O 5 : 0.2 to 1.0% by weight, MnO 2 , TiO 2 : both 0.2% by weight and x: 0.8, ε r: 46.6 to 47.9, Qu: 890 to 1300, τ f: -10.91 to -2.45 ppm/ °C. (2) At V 2 O 5 : 0.4% by weight, MnO 2 , TiO 2 : both 0.2% by weight and x: 0.8, ε r: 47.1, Qu: 1325, τ f: -7.46 ppm/ °C. (3) At MnO 2 : 0.2 - 1.0% by weight, V 2 O 5 : 0.4% by weight, TiO 2 : 0.2% by weight and x: 0.8, ε r: 47.0 to 47.5, Qu: 900 to 1440, τ f: -11.1 to -6.0 ppm/ °C. (4) At TiO 2 : less than 0.4% by weight, V 2 O 5 : 0.4% by weight, MnO 2 : 0.2% by weight and x: 0.8, ε r: 45.7 to 48.6, Qu: 750 to 1660, τ f: -10.2 to -1.1 ppm/ °C. (5) At TiO 2 : 0.1 to 0.2% by weight, V 2 O 5 : 0.4% by weight, MnO 2 : 0.2% by weight and x: 0.8, ε r: 46.4 to 47.1, Qu: 1320 to 1490, τ f: -8.8 to -7.5 ppm/°C. (6) At V 2 O 5 : 0.2 to 1.0% by weight, MnO 2 : not more than 1.0% by weight, TiO 2 : not more than 0.4% by weight and x: 0.8 to 0.96, τ f: -12 to +7 ppm/ °C, Qu: 800 to 1600, and ε r: 45 to 50. (3) Effect of the example in V 2 O 5 -MnO 2 -PbO system composition According to the results of Table 7 and Figs. 39 to 46 and Figs. 51 to 62, if V 2 O 5 is not added (No. 1 in Table 7), sintering is insufficient and measurement for each of the characteristics is impossible. Then, since τ f and Qu change by the addition (each in Fig. 41 and 40), τ f and Qu can be controlled. Particularly, since τ f increases along with the addition up to 0.6% and Qu increases along with addition up to 0.8% by weight, such addition is preferred. Further, ε r increases along with addition of MnO 2 (Fig. 43). Further, τ f increases along with addition up to 0.4% by weight (Fig. 45). Since Qu decreases by the addition, a great amount of addition is not preferred (Fig. 44). Since τ f changes along with addition of PbO (mainly in the negative direction), it shows that τ f can be controlled easily (Fig. 53). Further, since ε r increases with the addition, it is preferred (Fig. 51). Since Qu decreases with the addition, a great amount of addition is not preferred (Fig. 52). Further, since τ f changes greatly along with increase of the value x in Bi(NbxTa1-x)O 4 (mainly changes in the positive direction) (Fig. 57), τ f can be controlled by the change of the value x. Further, since Qu increases along with increases of the value x, it is preferred (Fig. 56). While the sintering density tends to be lower with the addition, 7.04 kg/m 3 sintering density can be ensured even if x is 1.0 (No. 29 in Table 7, Fig. 54). Further, referring to the sintering temperature, sufficient sintering is attained at 850 to 950 °C (Fig. 62) and physical properties are also stable (Figs. 59 - 62). Like that in the V 2 O 5 -MnO 2 -TiO 2 system composition. As described above, while each of the characteristics changes variously in accordance with the kind of each of the additives, the addition amount thereof and the sintering temperature, the following well balanced practical performances are shown, for example, within a compositional range shown below according to the results of this example (Table 7). For instance, the V 2 O 5 -MnO 2 -PbO system compositions exhibit the following well balanced practical performances. (1) At V 2 O 5 : 0.4 to 0.8% by weight, MnO 2 and PbO: both 0.2% by weight and x: 0.8, ε r: 44.9 to 46.8, Qu: 1460 to 1950, τ f: -14.5 to -1.7 ppm/ °C. (2) At V 2 O 5 : 0.6% by weight, MnO 2 and PbO: both 0.2% by weight and x: 0.8, ε r: 46.5, Qu: 1430, τ f: -1.75 ppm/ °C. (3) At MnO 2 : 0.2 to 0.4% by weight, V 2 O 5 : 0.4% by weight, PbO: 0.2% by weight and x: 0.8, ε r: 46.8 to 47.9, Qu: 1351 to 1465, τ f: -6.3 to -2.1 ppm/°C. (4) At PbO: 0.2 to 0.4% by weight, V 2 O 5 : 0.4% by weight, MnO 2 : 0.2% by weight and x: 0.8, ε r: 46.8 to 47.4, Qu: 1293 to 1465, τ f: -13.2 to -6.3 ppm/ °C. (5) At V 2 O 5 : 0.3 to 0.8% by weight, MnO 2 : 0.1 to 1.0% by weight, PbO: not more than 0.4% by weight and x: 0.8 to 0.96, τ f: -15 to +4 ppm/ °C, Qu: 1000 to 2000 and ε r: 44 to 49. The present invention is not restricted to the concrete examples as described above but variously modified embodiments can be made within the scope of the present invention in accordance with the purpose and application uses thereof.

Claims: A microwave dielectric ceramic composition comprising a composition represented by xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ) in which 0.45≦ x≦ 0.55 and 0 < y < 1.0 as a main ingredient, to which not more than 0.8 parts by weight (not including 0 part by weight) of V 2 O 5 is added and incorporated based on 100 parts by weight of xBi 2 O 3 -(1-x)(yNb 2 O 5 -(1-y)Ta 2 O 5 ). A microwave dielectric ceramic composition as defined in claim 1, wherein x is from 0.47 to 0.53, y is from 0.4 to 0.8, the addition amount of V 2 O 5 is from 0.4 to 0.6 parts by weight. A microwave dielectric ceramic composition as defined in claim 1 or 2, wherein the specific dielectric constant (hereinafter simply referred to as ε r ) is from 42.9 to 47.7, an unloaded Q (at 3.7 to 4.4 GHz, hereinafter simply referred to as Qu) is from 790 to 1490 and the temperature coefficient of a resonance frequency (hereinafter simply referred to as τ f) is from -46.4 to -16.2 ppm/°C. A microwave dielectric ceramic composition comprising a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 5% by weight (not including 0% by weight) of V 2 O 5 and not more than 2% by weight (not including 0% by weight) of PbO are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . A microwave dielectric ceramic composition as defined in claim 4, wherein x is from 0.2 to 0.9, the addition amount of V 2 O 5 is from 0.2 to 2.0% by weight and the addition amount of PbO is from 0.2 to 0.6% by weight. A microwave dielectric ceramic composition as defined in claim 4 or 5, wherein ε r is from 45 to 48, Qu (at 3.6 to 4.0 GHz) is from 960 to 1640 and τ f is from -47 to -36 ppm/ °C. A microwave dielectric ceramic composition comprising a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 5% by weight (not including 0% by weight) of V 2 O 5 and not more than 2% by weight (not including 0% by weight) of MnO 2 are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . A microwave dielectric ceramic composition as defined in claim 7, wherein x is from 0.2 to 0.9, the addition amount of V 2 O 5 is from 0.2 to 2.0% by weight and the addition amount of MnO 2 is from 0.1 to 0.6% by weight. A microwave dielectric ceramic composition as defined in claim 7 or 8, wherein ε r is from 45 to 47, Qu (at 3.6 to 3.9 GHz) is from 970 to 1640 and τ f is from -14 to -5.5 ppm/°C. A microwave dielectric ceramic composition comprising a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 2% by weight (not including 0% by weight) of V 2 O 5 and not more than 1% by weight (not including 0% by weight) of TiO 2 are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . A microwave dielectric ceramic composition as defined in claim 10, wherein x is from 0.6 to 0.96, the addition amount of V 2 O 5 is from 0.2 to 1.0% by weight and the addition amount of TiO 2 is from 0.1 to 0.6% by weight. A microwave dielectric ceramic composition as defined in claim 10 or 11, wherein τ f is from -30 to 0 ppm/ °C and Qu (at 3.3 to 3.9 GHz) is from 510 to 1160 and ε r is from 42 to 48. A microwave dielectric ceramic composition comprising a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which not more than 2% by weight (not including 0% by weight) of V 2 O 5 and not more than 2% by weight (not including 0% by weight) of MnO 2 , and not more than 0.7% by weight (not including 0% by weight) of TiO 2 are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . A microwave dielectric ceramic composition as defined in claim 13, wherein the addition amount of V 2 O 5 is from 0.2 to 1.0% by weight, the addition amount of MnO 2 is not more than 1.0% by weight and addition amount of TiO 2 is not more than 0.4% by weight and x is from 0.8 to 0.96. A microwave dielectric ceramic composition as defined in claim 13 or 14, wherein τ f is from -12 to +7 ppm/°C, Qu is from 800 to 1600 and ε r is from 45 to 50. A microwave dielectric ceramic composition comprising a composition represented by Bi(NbxTa1-x)O 4 in which 0 < x≦ 0.96 as a main ingredient, to which 0.2 to 1% by weight of V 2 O 5 , not more than 1% by weight (not including 0% by weight) of MnO 2 and not more than 0.5% by weight (not including 0% by weight) of PbO are added and incorporated based on 100% by weight of Bi(NbxTa1-x)O 4 . A microwave dielectric ceramic composition as defined in claim 16, wherein the addition amount of V 2 O 5 is from 0.3 to 0.8% by weight, the addition amount of MnO 2 is 0.1 to 1.0% by weight and the addition amount of PbO is not more than 0.4% by weight and x is from 0.8 to 0.96. A microwave dielectric ceramic composition as defined in claim 16 or 17, wherein τ f is from -15 to +4 ppm/°C, Qu is from 1000 to 2000 and ε r is from 44 to 49.

Inventors: KATAGIRI HIROSHI, OZEKI HIROFUMI, KATAGIRI, HIROSHI, OZEKI, HIROFUMI
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO. LTD.
Application year: 1994
Main classification: C04B35
IPC codes: H01G4, C04B35